The Apple Blog points to AT&T's GoPhone as the way to get into AT&T's network without signing up for a full service plan. Better still, the tweak that makes the iPhone work with the GoPhone's SIM card works on all versions of the iOS (2, 3, and 4), and doesn't require actually messing with your phone's firmware ("jailbreaking") or other warranty-voiding tweaks. Instead, you point your phone to a New Zealand-based unlocking site that does the proper changing of your Access Point Names (APN), and approve the changes it wants to make.

Lifehacker East lacks for an older iPhone to test the method out on, but given the links and pointers to the write-up, it's making us think about peeking around Craigslist and looking to see what older iPhone models are out there. Sometimes, all you need is a little data while you're out and about, and this fits that bill pretty nicely.